This study is concerned with the systematic investigation of the molecular mechanisms by which folate deficiency interferes with normal orofacial development and growth. Rabbit palates will be cultured under conditions of folate deficiency induced by the use of the folate antagonist methotrexate, enzymatically by the use of Carboxypeptidase-G1, or through the use of folate deficient media. Dihydrofolate reductase activity, folate pools, nucleic acid and protein synthesis will be measured in experimental and control tissues. The distribution of 3H-MTX as well as the intracellular localization of dihydrofolate reductase will also be determined. All biochemical parameters will be correlated with morphological observations (macroscopic, microscopic including mitotic indices and ultrastructural). Correlation of morphological changes with underlying molecular mechanisms, under the controlled in vitro conditions, in a known target tissue of folic acid deficiency teratogenesis, will clearly define specific sites and mechanisms of teratogenic action involved in folate deficiency orofacial dysgenesis. This investigation would enhance present knowledge of how and at what stages in the developmental process altered control mechanisms exert their influence, and would be of considerable significance in future studies directed toward the elucidation of those factors responsible for formation of cleft palates.